A team at Mississippi State University performed a detailed experimental analysis of diesel–ignited propane dual fuel combustion on a 12.9-liter, six-cylinder, production heavy-duty diesel engine. They presented their results Results are presented for brake mean effective pressures (BMEP) from 5 to 20 bar and different percent energy substituted (PES) by propane at a constant engine speed of 1500 rpm.

The gaseous propane was fumigated upstream of the turbocharger air inlet and ignited using direct injection of diesel sprays.

With stock engine parameters, the maximum propane PES was limited to 86%, 60%, 33%, and 25% at 5, 10, 15, and 20 bar BMEPs, respectively, either by high maximum pressure rise rates (MPRR) or by excessive HC and CO emissions.

With increasing PES, while fuel conversion efficiencies increased slightly at high BMEPs or decreased at low BMEPs, combustion efficiencies uniformly decreased. Also, with increasing PES, NOx and smoke emissions were generally decreased but these reductions were accompanied by higher HC and CO emissions.

Exhaust particle number concentrations decreased with increasing PES at low loads but showed the opposite trends at higher loads. At 10 bar BMEP, by adopting a different fueling strategy, the maximum possible propane PES was extended to 80%.

Comments

The Motiv engine concept is a potential HD engine that can use 100% gaseous fuels such as methane, propane and even H2 using compression ignition w/out requiring diesel fuel injection, and having very high efficiency. These are accomplished by using ultra-high compression ratio of 56 and a compound engine layout running 2-stroke cycle.

The real low hanging fruit may be naptha and LPG, which are severely underutilized as fuels. In any case, I thought the rationale for dual fuel engines is switchability: diesel for range, gas for availability and quick warm-up.